Mechanical flat-lead pencil



May 31, 1960 H. BACHMANN MECHANICAL FLAT-LEAD PENCIL Filed Jan. 20, 1956 7 2,] I M :NAANAARNAfi VVRMQ? JA/Vf/VTOR:

f/a ra la! ,BacAmann Pa fe A gent United States MECHANICAL FLAT-LEAD PENCIL Harald Bachmann, Stein, near Nurnberg, Germany, as-

signor to A. W. Faber-Castell, Stein, near Nurnberg, Germany, a firm of Germany The present invention relates to improvements in drawing pencils, and more particularly in mechanical pencils using fiat leads.

For adjusting a flat lead in a pencil as known prior to this invention the lead had to be advanced either through its own gravity or by screwing it forwardly. In either case, such adjustment of the flat lead required a change of the drawing position of the hand holding the pencil, and after each adjustment the draftsman had to readjust his grip on the pencil to realize the advantage of the flat lead, as well as his hand to its proper drawing position relative to his work. To an eflicient draftsman, such frequent adjustments meant a considerable annoyance and reduction of his work output. 7

It is an object of the present invention to overcome these and other disadvantages of the prior fiat-lead pencils and to provide a mechanical pencil, the fiat lead of which may be easily adjusted during the course of work without requiring any change in the proper drawing position of the hand holding the pencil.

, Another object of the invention is to provide a pencil holder or casing with a tubular lead guide which encloses the fiat lead and is rotatable in the pencil casing.

For adjusting the lead of a pencil according to this invention 'the tip of the projecting end of the lead-guiding tube may, for example, be gripped between the thumb and index finger of the left hand while the pencil casing will be turned at the same time to advance the lead. Another method of adjusting the lead consists in resting the fiat lead-guiding tube against a ruler or similar drawing tool and holding it with a finger of the left hand against such tool so as not to turn while the pencil casing is being turned. Or, the normally bent index finger of the drawing hand holding the pencil near its tip may, without any change of the drawing position of that hand, be stretched to hold the lead-guiding tube against rotation or to press it against a ruler or other drawing tool, while the left hand is eased to turn the pencil casing to advance the lead.

An important feature of the invention consists in pro viding a key-shaped member within the fiat lead-guiding tube which is slidable therein in axial direction to act upon a flat lead to slide the same within the tube. To carry out such axial movement, the key-shaped member has bitlike projections extending transversally to the axis which are in engagement with a helical thread on the inner wall of the tubular pencil casing. The keyshaped member preferably consists of a flat slide bar of .a shape substantiallycorresponding to that of the leadguiding tube and is adapted to slide easily therein. Within the longitudinal area of movement of the bitlike projections of the key, the lead-guiding tube is provided in one of its narrow sides with a slot through which the projections extend toward and into engagement with the helical thread. Since the key is thus axially slidable but non-rotatable, a turn of the pencil casing together with the helical thread therein will slide the key within the lead-guiding tube either toward the tip or the upper end of the pencil. When sliding toward the tip, the key will atent a 2,938,498 Patented May 31, 1960 ice the tube if, for example, the lead should be worn off to the outer end of the tube. This compression spring surrounds the lead-guiding tube concentrically and rests with one end on the lower end of the helical thread in the pencil casing, and with the other end on suitable lateral projections on the tube. These projections may be formed on the tube, for example, by endwise compression and by thus producing an outward bulge, or by securing a small washer on the tube in any suitable manner. To afford a firm support for the spring, a washer of suitable diameter may also be interposed between each spring end and the respective point of support.

Another important feature of the invention consists 1n the provision of a pair of elongated supporting bars or strips which have rounded outer surfaces and substantially flat inner surfaces to rest upon the opposite flat sides of thelead-guiding tube so that, with the guiding tube between them, they have a substantially circular cross section. The forward ends of these supporting bars are guided within the tip of the pencil, and preferably so as to project therefrom, while the rear ends are guided within the pencil casing. Particularly near then forward ends, the supporting bars are held in firm engagement with the lead-guiding tube so as to reinforce the same and prevent it from bending.

Another feature of the invention consists in making the lead-guiding tube of a length so as to extend nearly to the rear end of the pencil. Such a long tube has the advantage that it permits the insertion of very long leads which last for a considerable time.

Still another feature of the invention consists in making the pencil casing and the helical thread therein of one integral piece of material rather than of two separate pieces which are secured together. The helical thread may in such case form a helical groove along the inner wall of the pencil casing.

Further objects, features, and advantages of the present invention will appear from the following detailed description thereof, as well as from the accompanying drawings, in which Fig. 1 shows a mechanical flat-lead pencil according to the invention in a section taken in the axial direction thereof;

Fig. 2 shows a similar axial section through the upper end of the pencil, but turned about its axis to illus trate the key-shaped slide bar; I

Fig. 3 shows a cross section taken along line IIIIII of Fig. 2;

Fig. 4 shows a cross section taken along line IVIV of Fig. 1; while Fig. 5 shows a perspective view of the mechanical flat-lead pencil according to the invention and one of the methods of adjusting the same;

Fig. 6 shows an axial section similar to Fig. 2 through the upper end of a modified pencil according to this invention.

Referring to Figure 1 of the drawing, the new mechanical pencil for flat leads comprises a tip 1 attached to a pencil casing 3 by means of a thread case 2. .A central bore 4 and a bore 5 are provided in the tip \1 and in the casing 3, respectively, and are adapted to receive a tubular guide 6 of rectangular cross section for a flat lead 24, a helical member 7 and a compression spring 8.

The lead guide 6 is displaceably held in the tip 1 between two supporting or clamping bars 9 and'li] which, according to Figure 4, have round outer faces, while their inner surfaces frictionally engaging and enclosing the lead guide are fia T s l u de is a pt d o be d splaced upwardly by overcoming the force of the helical compression spring 8 surrounding it. The upper end of this spring 8 rests on a washed 11 in the pencil casing 3 which, in turn, rests on the lower end of the helical member 7, fixedly held in the pencil casing 3. The lower end of the spring ,8 is seated on a washer 12 which, in turn, rests on an annular flange 14 forming a contraction in the bore '5 of the pencil casing 3.

As shown in Figure l, the lead guide 6 has small pro trusions or projections 13 on its outer surface at the level of the washer 12, said projections 13 engaging the lower face 15 of the washer 12 and the front surfaces 16 and 17 on the upper ends of the supporting or clamping bars 9 and 10, respectively. Thus, these projections 13 forming abutments' for the washer 12 and the clamping bars 9 and =10 of the lead guide 6 are holding the latter in the position illustrated in Figure 1.

The lead guide 6 can be displaced upwardly, i.e., inwardly with respect to the tip 1 and pencil casing 3, by applying pressure to the lower end of this lead guide, for example, by pressing it with its outer end on a writing surface and thereby pushing the lead guide upwardly with respect to andin the tip 1 and the casing 3. The pressure force applied during such operation is transinitted via the protrusions 13 and the washer 12 to the helical spring 8 whereby the latter is compressed. When the pressure is released, the lead guide 6 is returned to its initial position shown in Figure l by the action of the compression spring 8. The lead guide tS'is prevented from being pulled out from the pencil casing by the provision of the protrusions 13 seating on the front surfaces 16 and 17' of the supporting or clamping bars 9 and 10 mounted in the tip '1 and the pencil casing 3. The clamping bars '9 and 1d are retained in the tip 1 by means of flanges 18 and 19 on the outer surfaces of these bars 9 and 10, respectively, said flanges abutting an annular shoulder '20 in the bore 4 of the tip 1 and thereby assuring a firm mounting of the bars '9 and *10' in the tip .1, while, at the same time, permitting rotation of the bars 9 and together with the lead guide *6 and the inserted lead 24 with respect to the tip 1 and the casing 3.

The upper end of the helical members 7 is connected to the pencil casing 3 by means of a knob 12 screwed in the upper threaded end of this casing.

As illustrated particularly in Figs. 2 and 3, a key or slide bar 21 is guided within the upper end of lead guide 6 which is provided with a longitudinal slot 23 in one of its narrow sides through which the bitlike projections 22 extend so as to engage into the helical groove in helical member 7. The flat lead 24 which is held in lead guide 6 may be adjusted by an axial movement of key 21 against the upper end of the lead.

' The operation of the new mechanical fiat-lead pencil is as follows:

If the pencil is held as shown in Fig. and turned in the direction of the arrow, lead guide 6 will be moved relative to tip 1 of the pencil. Lead guide 6 being firmly held by the left hand of the user, key 21 which engages with helical member 7 by the projections 22 then shifts within lead guide 6 in an axial direction and advances lead 24 outwardly. For returning the lead, casing 3 only needs to be turned in the opposite direction so that key 21 will slide upwardly. Lead 24 may then be pushed into lead guide 6 by a slight pressure upon the tip 25 of the lead. Since lead guide '6 extends almost through the entire length of the pencil, it permits the use of very long leads.

If it is desired to reduce the number of parts necessary for making the pencil, the latter may be designed according to the modification of Figure 6 without providing the helical member as a separate element secured to the casing. According to Figure 6, the helical member is made an integral portion 7 of casing 3' by cutting a helical groove 27 into the inner wall of this casing.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. A mechanical pencil for flat leads comprising a pencil casing having abutment means, a tip on the front of said casing, a single-piece tubular lead guide including abutment means rotatably mounted in said casing and protruding from said tip with outer and inner rectangular cross section throughout its length, guiding means for said rotatable movement of said lead guide in said casing at least at the front end of the latter, including a pair of supporting bars on opposite sides of said fiat lead guide, having round outer contours and flat inner faces and being rotatably mounted in said tip and said casing between said abutment means for avoiding axial displacement, said lead guide being clamped and held be tween said inner faces of said supporting bars by frictional engagement with the two wider sides of said lead guide, while said round outer contours permit rotation with frictional engagement between the contacting faces of said supporting bars and said tip during their rotatable movement to each other, a fiat lead, a fiat slide bar arranged behind said lead, said lead and slide bar being slidably disposed within said lead guide, a sleeve-like guide body with helical grooves surrounding said lead guide within said casing and secured thereto, a longitudinal slot in said lead guide, at least one lateral projection on said slide bar traversing said longitudinal slot of said lead guide and engaging in said helical groove for axial displacement of said slide bar and said lead by rotation of said casing with respect to said lead guide, and elastic means in said casing between the latter and said lead guide to resiliently oppose displacements thereof in axial direction.

2. A mechanical pencil according to claim 1, wherein said abutment means respectively consist of lateral protrusions at said lead guide and inwardly directed projections of said casing opposite said protrusions, one side of said protrusions and opposite projections forming abutments forsaid supporting bars and the opposite side of said protrusions and projections forming abutments for said elastic means between said lead guide and said casing to permit restorable axial displacements of said lead guide towards the rear by applying pressure to its front endyand wherein washers around said lead guide are disposed at both ends of said elastic means between the latter and the respective opposite abutments.

3. A mechanical pencil according to claim 1, wherein said abutment means respectively consist of lateral protrusions at said lead guide and inwardly directed projections at the inside of said casing opposite said protrusions, serving at one side as abutments for one end of said supporting bars, and a compression spring bearing with one end against said protrusions and projections,

the other end of said spring abutting against said sleevelike helical-lygrooved guide body, and intermediate washers around said lead guide at both ends of said spring between the'latter and the opposite abutment parts.

Ref r nces Ci ed. in the. file or this patent UNITED STATES PATENTS 

